package nowCoder;

import java.util.Scanner;

/**
 * @Auther: zzx
 * @Date: 2024.03.24/3/10
 */
public class HJ100 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println((2+(3*n-1))*n /2);
    }
}
